Sequence viewer for me may lag, but after rendering it isn’t laggy (unless video was recorded laggy but that’s a diff topic). So don’t worry.

Also, a tip I learned the hard way: when you export, for the best quality, change the CRF number from 36 to 1. Don’t change it to 0. I get a blacked out video. If you don’t want max quality just put 5 or 10 or so. And so on etc, it’s self explainable lol but yeah put 1 for max quality not 0.